This invention relates to textile fibers and filaments of linear terephthalate polyesters, and is more particularly concerned with products of polyesters modified with basic nitrogen-containing groups to provide improved dyeability with acid dyes.
Although many methods have been tried for improving the acid-dyeability of such polyester fibers and filaments by copolymerization of nitrogen-containing modifiers into the chains of polyester molecules, such previous attempts have not provided adequate solutions to the problem for various reasons. In order to provide good dyeability with acid dyes, the modifier should contain a highly basic nitrogen atom which is suitably positioned as a dye site but which does not form a reactive center for polymer degradation reactions. That is, the basic modifier should be compatible with the polyester and should not result in objectionable discoloration or inadequate molecular weight. The modifier should have sufficient thermal stability for incorporation in the polyester during condensation polymerization and for melt-spinning into filaments. The amount of modifier required for good dyeability should not be so great as to dilute desirable physical properties of the polyester, and the modifier should have low volatility to prevent escape with low-boiling compounds removed during the condensation polymerization. The melt-spun filaments should retain a high level of dyeability when subjected to heat-setting treatment after drawing. The dyed filaments and fibers should have good dye-lightfastness and resistance to removal by washing or dry cleaning.